Single cylinder (and twin cylinder) petroleum fueled internal combustion utility engines are used in a variety of applications by homeowners, tradesmen and others. Utility engines are ordinarily produced in two fundamental familial types, e.g., "two cycle" and "four cycle" (viz, "two stroke" and "four stroke"). Each of these engine types operate with four cardinal events, including: 1) INTAKE, 2) COMPRESSION, 3) COMBUSTION and 4) EXHAUST. However the two cycle engine achieves these four events in one revolution or two strokes of the crankshaft (i.e., one piston downstroke and one piston upstroke) while the four cycle engine requires two crankshaft revolutions and four strokes (i.e., two piston downstrokes and two piston upstrokes).
While the two stroke engine is decidedly simpler design (and manufacture) it requires mixing and storage of a special fuel and oil mixture. In fact it is arguable that a two cycle engine may have merely three moving parts: the crankshaft, connecting rod and piston with perchance room for quibble over whether the reed type intake valve ordinarily used with Small engines is a moving part or not. Other drawbacks for two cycle engines include a lack of good lugging ability, low efficiency, pollution considerations and compromised reliability under extended operation. Two cycle engines are also ordinarily designed to operate with relatively high crankshaft speed r.p.m. to achieve reasonable efficiencies and output power, but with relatively poor speed regulation and relatively high noise level. Furthermore, high crankshaft r.p.m. also translates into increased mechanical wear. Two cycle engines are most economical in small horsepower ratings and rarely are they built in multicylinder versions. In spite of these drawbacks two cycle engines find widespread application in chain saws, string type weed cutters, small lawnmowers, outboard boat motors, snow mobiles and the like.
Four cycle engines, on the other hand, tend to be preferable when long term reliability, durability and stable performance is a criteria. Operation from ordinary gasoline, alcohol or "gasahol" affords simple fuel needs (i.e., no fuel-oil mixtures). Four cycle engines may be produced to operate well at low crankshaft speeds (under 2,000 r.p.m.) and with excellent speed constancy in applications such as engine driven alternator sets where speed control is all-important in order to stabilize the frequency of the delivered power. A vast majority of small four cycle engines finding use in everyday application in the home and on the job more suitably operate in the 3,000-4,000 r.p.m. range, which has been demonstrated as an optimal trade-off between speed, engine bulk, mechanical life, or in a more practical sense, in engine cost. Small general purpose four cycle engines are produced in single and multiple cylinder models and with popular horsepower ratings more or less between about 3 and 15 horsepower find wide application on lawnmowers, small tractors, generator sets, pumps and a myriad array of other such workaday applications where stable and long term performance are vital.
Small engines of this type, either 2-cycle or 4-cycle in principle construction, categorically suffer from frequent application in machines where they encounter long periods of non-operation. For example, Winter storage of a lawn mower or tiller leads to non-usage for many months. Likewise, seldom used "standby" electric power generators find long periods of shut-down, sometimes even years of sitting without a startup. Machines such as a homeowner's chain saw and tiller find infrequent usage and seasonal machines such as snow blowers, snow mobiles and the like may go for 6-9 months or more without startup. In each of these cases, where an engine is stored for long intervals without use, immediate startup on demand is unlikely and becomes progressively more difficult as the engine's age increases.
In recent times, the federal government's Environmental Protection Agency (EPA) and Department of Energy (DOE), as well as state environmental agencies, have contrived a collection of rules and regulations pertaining to fuel quality, exhaust emissions and other factors which are the anathema of carbureted internal combustion engines. Contemporary "blended" gasoline meeting general fuel requirements for reduced volatility is particularly troublesome to small engine design. Due to cost restraints, simplicity has been the goal of carburetor design for years. Furthermore, easy and relatively "foolproof" operation by users has dictated that a carburetor should have few (if any) adjustments which has led to total compromise between start-up and running mode design requirements for the carburetor. In other words, if the engine doesn't quickly start, there is not much which the ordinary user can do to enhance the possibility for startup. From the overall market viewpoint, such simplicity is desirable since the end-user of the engine is frequently totally inept as a mechanic and any available adjustments would, in most cases, merely reduce the liklihood for successful engine startup. More to the point, however, is that in order to meet the goal for emissions reduction, carburetor settings need to be fixed within narrow bounds and the only assurance a manufacturer has that such bounds will be maintained is to effectively "seal" or restrictively pre-set as many of the carburetor adjustments as possible. As a result, carburetion on a contemporary small engine becomes simply a "go or no-go" proposition with little, if any, possibility for "tweeking" the carburetor to better the chances for cold startup.
Combining these simplified prior-art carburetor designs with infrequent engine usage leads to difficulty in achieving quick engine startup which may be due in part to a total evaporation of any residual gasoline vapors which might otherwise stimulate engine startup. In addition, the reduced volatility of the mentioned blended-gasoline fuels which are now being produced (which exhibit an exceptionally low amount of volatile ingredients) leads to difficulty in getting gasoline "fumes" to draw through a typical small engine carburetor especially at the relatively low cranking speeds characteristic of such engines and particularly when using a common rope-start (e.g., "recoil-start") mechanism.
A direct implication of these various factors of carburetor simplicity, fuel blending and exhaust emission considerations is that quick and reliable start-up of small gasoline engines is becoming more and more problematic. As a result of the increasing need for achieving better start-up of these kinds of small engines, I have conceived an easy to use and inexpensive approach for introducing a supply of priming fuel directly into the engines intake port whereby engine start may be expected to Occur with the first pull of the starting rope.